Biodegradation of organic compounds during co-composting of olive oil mill waste and municipal solid waste with added rock phosphate

Liquid and solid olive oil mill waste was treated by composting in a mixture with the organic part of municipal solid waste and rock phosphate. The transformations that occurred during the process were evaluated by physical, chemical and spectroscopic analyses. After five months of composting, the final compost presented a C/N ratio under 20, an NH4+/NO3- ratio under 1 and a pH around neutral. A high level of organic matter decomposition paralleled a notable abatement of phenols and lipids. The results show the effective dissolution of mineral elements during composting. This transformation was followed by Fourier transform infrared which showed a decrease in the absorption bands of aliphatic bonds (2925 and 2855 cm(-1)) and carbonyls of carboxylic origin (1740 cm(-1)). In addition to the increase in humic substances and the improvement of germination indices, the parameters studied confirm the stability and the maturity of the composts. The absence of phytotoxicity opens the way to agricultural spreading.